AMD Radeon HD 7870 & HD 7850 Review

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With today’s release of the HD 7870 and HD 7850, AMD has achieved their goal of having a complete top to bottom desktop graphics card lineup based upon the new GCN architecture. Some of their cards have met with absolute success while others didn’t quite live up to expectations on the pricing front but for the most part, AMD’s HD 7000-series cards provide an excellent combination of performance and efficiency.

These two new entries into the lineup are meant to effectively bridge the gap between the high end and entry level markets. For many the HD 7700 series simply doesn’t provide enough performance in today’s games and the HD 7900 cards are too expensive to fit into most gamers' limited budgets. The comfortable middle ground between these solutions was previously bridged by NVIDIA’s numerous GTX 560 Ti versions alongside AMD’s own HD 6800 series but that all important position is now being taken up by the so-called “Pitcairn” architecture.

Upon first glance AMD’s new mid range product stack looks to be quite simple but there is actually some overlap with cards from the previous generation. The HD 7870’s 20 Compute Units which play host to 1280 Stream Processors put it well above the older HD 6870’s capabilities but more importantly, the 80 texture units put theoretical performance closer to the outgoing HD 6900-series rather than any of the popular Barts-based cards. With an engine clock of 1GHz working in tandem with the GCN architecture's inherent rendering efficiency, AMD is betting their Pitcairn XT will provide a natural upgrade path for anyone still holding onto a HD 5870 or looking to step up from the HD 6870. It does lag a bit behind the Cayman architecture in terms of memory speed but with 2GB of GDDR5 operating at 4.8Gbps, bandwidth almost certainly won’t be a concern. A price of $349 also puts the HD 7870 close to the HD 6970’s initial asking price of $369 so it obviously has some big shoes to fill.

The Pitcairn Pro –or HD 7850- doesn’t have such lofty expectations but with a cost of $249 it lines up with some legendary products from years past. The HD 6870, GTX 460 1GB, GTX 560 Ti and many cards from previous generations were launched at this critical price point and all went on to sales success. With 1024 cores coupled with 64 TMUs and 32 ROPs, the HD 7850 seems to have what it takes to stay competitive. More importantly, this happens to be the first sub-$300 card to boast 2GB of memory operating on a 256-bit wide bus which should make it a great solution for a market that’s accepted 1080P PC monitors as a de facto standard.

AMD certainly has a rosy outlook when it comes to comparing the HD 7800-series with NVIDIA’s incumbent 500-series. According to their predictions the $349 HD 7870 should handily beat the GTX 570 while the HD 7850 has been tasked with the goal of putting the popular GTX 560 Ti to shame. No mention was made of the recently released GTX 560 Ti 448 but we’ll still include it in our performance charts for comparison’s sake.

NVIDIA hasn’t even found it necessary to cut the price of their GeForce lineup since the GTX 570 retails for about $349 without rebates, the GXT 560 Ti sits at $190 and GTX 560 Ti 448 still retains its launch price $289. Rather than causing their competition to react to pressure on the pricing front, AMD is confident that consumers will see the value of their solution over what’s being offered by NVIDIA.

The $249 to $349 bracket is constantly referred to as the graphics market’s “sweet spot” and AMD is quite obviously hell bent on staking their claim to it. Plus, having their whole lineup based on $100 increments should also give them plenty of wiggle room if price cuts are needed sometime down the road.

There are however some wrenches thrown into the works. Not only is the competition going to be fierce but the HD 7800 series won’t be actually available until March 19th (or later according to some board partners). Usually we prefer to see a hard launch since without one, the competition could in theory adjust their prices to compensate for any performance discrepancy even before the new cards are widely available. So AMD may be taking a risk but regardless of the final outcome these new cards could be precisely what everyone has been waiting for.

 

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AMD’s Pitcairn Core Under the Microscope

AMD’s Pitcairn Core Under the Microscope

Upon first glance the 2.8 billion transistor Pitcairn core bears a striking resemblance to that of the higher end Tahiti and you’d be forgiven if you thought that it is nothing more than a HD 7950 with a few bits and pieces disabled. Naturally, that isn’t the case since Pitcairn has been built from the ground up to be an efficient money maker for AMD and as such, a brand new design was needed. In its fully enabled form it makes use of 20 Compute Units containing 64 Stream Processors and four texture units for a total of 1280 cores and 80 TMUs. These are then broken into two distinct processing engines, each of which holds 10 CUs .

Aside from the primary processing stages, the render output pipeline mirrors AMD’s higher end cores with eight combined Render Output Units containing 32 ROPs. The real differentiating factor between Pitcairn and previous generations of mid level cards lies within its memory controller layout. Instead of using a simple 128-bit or 256-bit bus paired up with 1GB of memory, this architecture is designed to be used in parallel with 2GB of GDDR5, giving it plenty of bandwidth. We’re guessing that 1GB versions will likely be used to plug the hole between the HD 7870 and HD 7850 at some later date.

Speaking of the HD 7850, it uses the Pitcairn Pro core which essentially mirrors its higher end sibling but comes with a quartet of Compute Units disabled. The result is a still respectable 1024 cores and 64 texture units but otherwise, the memory, ROP and cache hierarchy is identical to a fully enabled part.

There doesn't seem to be much different between the geometry processing engines in the current and next generation architectures but there are several optimizations built into Pitcairn for increased efficiency and throughput.

Let’s start with the obvious first. Much like Cayman and unlike the lower end Cape Verde, Pitcairn uses two distinct geometry and primary processing engines that are accessed through a common Command Processor which takes care of load balancing and scheduling. This is a major distinguishing factor between this architecture and Barts since the outgoing HD 6800 series only had a single graphics engine that allowed it to only process one primitive per clock. Pitcairn on the other hand can attack higher levels of geometry with two engines working in parallel.

The fixed function stages are broken up into the two engines that work in parallel and contain what AMD calls their “ninth generation” tessellators. Alongside other small changes, these new tessellation units still feature off-chip buffering which allows geometry data from tessellated workloads to be stored in the DRAM if the on-chip cache becomes saturated.

Largely due to the addition L2 cache (in this case 512KB) and other improvements in the tessellation engine, there is a vast improvement over the HD 6900-series at higher levels of tessellation. Many people may clue into the seemingly lackluster increase at lower levels but we have to remember that the previous architecture already brought a ton of potential to the table in exactly these situations. Once everything is taken into account, Pitcairn should offer more balanced performance in DX11 games that demand all levels of geometry processing and can in essence compete on an almost level footing with NVIDIA’s GTX 500-series.

 

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PowerTune and ZeroCore Power Technologies

PowerTune Technology

One of the largest challenges GPU manufacturers face is the rapid increase in the power consumption of their higher-end ASICs. NVIDIA’s solution to cut consumption and TDP in their GTX 500-series was a combination of input current monitoring and upgraded heatsinks along with application detection. AMD meanwhile took a different path with their PowerTune technology. It uses a complex set of concurrent calculations to determine on-the-fly TDP levels so clock speeds can be adjusted once the card reaches a pre-determined maximum thermal design power level.

The entire point of PowerTune is to allow AMD to strike a delicate balance between power consumption, thermals and clock speeds. If such a middle-man didn’t exist, the clock speeds many AMD GPUs would have been significantly lower since there would have been nothing to keep TDP in check. As one might expect, PowerTune makes a comeback in the Pitcairn cores and it still behaves in the same way as before.

A typical GPU will likely be used in any number of applications but its primary focus will usually be upon one thing: entertainment. While there are several synthetic benchmarks which cause a graphics card to consume copious amounts of power, most typical games will never even begin to approach these levels. As such, AMD has focused their PowerTune technology upon scenarios which put unrealistic loads upon the GPU rather than games. Since most of us don’t sit around all day benchmarking with 3DMark, this is good news.

Unfortunately, depending on their rendering methods there may still be the odd game which will be caught up in the crossfire and have its performance capped but we will be tackling this potential issue in a later section. It is just important to remember that AMD has tuned this technology to deliver the best gaming performance while weeding out potential power viruses.

As AMD describes it, this new technology is simply used to contain power consumption in such a way that the actual TDP of a given product will in effect determine clock speeds. Instead of letting the card run amok for the few seconds of absolute peak consumption that will likely occur every now and then, PowerTune caps power draw through clock speed modification. After the peak periods are concluded, clock speeds along with performance will return to normal.

This may all sound like doom and gloom for overall performance but PowerTune is actually designed for a worst-case scenario rather than a typical usage pattern. The algorithm to determine implied power consumption is based upon an extremely high leakage ASIC operating with 45 degree inlet temperature. Remember that high temperatures increase power draw in transistors so this ensures products are not artificially capped in lower temperature scenarios. Since TDP is the determining factor here, if you keep your card cool within a well ventilated case you should in theory never see PowerTune kick in while gaming. According to AMD, it has also allowed them to drastically increase the clock speed of their cards since PowerTune allows for better TDP predictability.

ZeroCore Power

One of the issues with most modern graphics cards is their power consumption when not actively driving 3D graphics content or accelerating certain applications. Even if your monitor is turned off, the only way of conserving electricity is to put the system to sleep or allow it to hibernate. Granted, when in idle mode a GPU doesn’t consume all that much power but a constant 30W over long periods of time can sure add up on a monthly power bill. This is where ZeroCore Power steps into the equation.

The basic idea behind ZeroCore Power is to effectively shut down the card during periods when the GPU isn’t outputting an onscreen image. These “long idle situations” are determined by Windows which is programmed to shut off your display after a preset amount of time (you can access it by going into the Display Power Options and choosing when Windows can turn off your display) in order to optimize full system efficiency. AMD’s driver will detect this and put the graphics card into a suspended sleep mode by shutting off the fan and powering down non-essential onboard components. It will then wake back up the moment Windows detects an input and activates the display again.

AMD hasn’t stopped there either. Pitcairn features power saving features like engine clock deep sleep and a DRAM stutter mode (which compresses any residual contents within the framebuffer) in order to further reduce standard 2D power consumption to a mere 10 to 12 watts.

Where ZeroCore Power technology really comes into its own is in Crossfire setups, even though the Pitcairn products are only compatible with dual card setups. Since only one GPU is driving the display at all times, any additional cards are automatically put into ZeroCore mode, even when in standard idle conditions. The result is drastically lower idle power consumption numbers for systems with more than one GPU. Meanwhile, in long idle situations, even the primary graphics card is put into a suspended sleep mode as well.

 

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Advanced Image Quality, PRT & New AA Modes

Advanced Image Quality

Much has been said about AMD’s claims of leading edge texture filtering quality on the HD 6000-series but for the most part, it was an improvement over previous generations. Whether it was up to expectations is still open for debate but the Southern Islands family is once again claiming to have virtually eliminated the flickering and artifacts that sometimes appear in games.

In order to high the high note in terms of texture filtering, Southern Islands cards feature an improved anisotropic filtering algorithm that’s designed to virtually eliminate shimmering in high resolution textures. This may sound like a tall order to fulfill but after seeing it in action, we’re confident AMD can deliver this time around.

One of the beauties of this new filtering algorithm is its ability to run without additional buffering so there is no drain on system resources. In addition, it is automatically enabled to gamers should see vastly improved image quality without having to dive into the Catalyst Control Panel.

Introducing PRT (Partially Resident Textures)

One of the main challenges for today’s GPUs is how to handle large amounts of high resolution textures when moving through a scene. Presently, when a player moves through a game environment the texture information in upcoming frames is constantly loaded between the disk, CPU and the graphics card. Usually the effect of this preloading is seamless but as larger amounts of information are loaded, stuttering can occur.

AMD’s solution to this somewhat complex problem is to leverage the local memory on the GPU and allow it to act as a true texture caching system. Essentially, upcoming textures are prefetched from the CPU and disk and stored locally on the GPU until they are ready to be used by the application. In a way this can almost be considered a form of texture “streaming” and should help eliminate the stutter normally associated with scene loading.

In addition to preloading, PRT can also dynamically load selected textures based on when they will be needed instead of loading every bandwidth-hogging texture all the time. This should help eliminate the memory footprint the feature requires.

Unfortunately for gamers Partially Resident Textures technology is application controlled so it has to be built into a game engine before it can be utilized. Supposedly, AMD’s development team is working with game developers to include this feature in upcoming releases but there aren’t any titles on the horizon that will put it to good use.

New Anti Aliasing Modes: MLAA 2.0 & SGSSAA

Morphological AA or MLAA was introduced by AMD back when the HD 6870 was first announced. In a nutshell it is form of fullscreen anti-aliasing that delivers an image quality which is comparable to Super Sample AA, but can be implemented with a fraction of SSAA’s performance hit. The AA algorithms are calculated more efficiently by leveraging GPGPU compute abilities alongside Microsoft’s DirectCompute API. Since the post-processing filtering is done by DirectCompute, the whole scene can be quickly analyzed so this AA method isn’t limited to only certain aspects of a given image. One of the more interesting benefits of Morphological AA being done through a standalone API is the fact that it can be used for both 2D and 3D scenes. Thus, it can be applied to things like video, Flash apps and more. In addition, since it is controlled directly through AMD’s Catalyst Control Center and makes use of DirectCompute, Morphological AA has the ability to be forced in any DX9, DX10 or DX11 game.

Unfortunately, one of the tradeoffs was lower performance but with the introduction of MLAA 2.0, quality has been slightly improved while system resource requirements have been minimized. The result should be better image quality without a significant impact upon in game performance.

Starting in the 12.3 beta due out later this month, AMD will be including yet another anti aliasing routine into their Catalyst Control Center’s bag of tricks. Sparse Grid Supersampling Anti Aliasing or SGSSAA has been a hot topic on game developer boards since it allows for ultra high image quality through the use of advanced AA techniques.

In layman’s terms, SGSSAA is meant to calculate each individual frame as a whole as opposed to MSAA’s method of analyzing polygonal edges and applying a simple AA mask. Not only does this approach allow for a dynamic level of detail but all elements of a scene receive anti aliasing which includes textures, polygon edges, shadows and shader modules. Unfortunately, these types of calculations take a massive amount of horsepower but the tradeoff should be some of the most realistic in game scenes we’ve experienced.

 

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A Closer Look at the HD 7870 2GB GHz Edition

A Closer Look at the HD 7870 2GB

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The HD 7870 2GB is designed in such a way that it meshes with the rest of AMD’s HD 7000-series. That means it incorporates a simple blower-style heatsink setup which is covered with a predominantly black shroud. A few touches of ATI…errr…AMD red are added for good measure and the effect is once again quite striking but this time in a more compact 9 ¾” length.

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With an estimated power consumption of about 175W and a fair amount of overclocking headroom, the HD 7870 is equipped with a pair of 6-pin power connectors. These are surrounded by an anodized aluminum frame that runs the card’s length and is supposed to help with heat dissipation.

Unlike the HD 7900-series, the HD 7870 uses a single Crossfire connector meaning it is limited to dual card configurations only. AMD has also eliminated the BIOS switch in order to cut costs and leave enthusiast features for their ultra high end products.

The backplate output connectors have remained the same as on every other Southern Islands card (except for the pint sized HD 7750) with connectors for DVI and HDMI 1.4 alongside two mini DisplayPorts.

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As usual, there really isn’t all that much to see by flipping this card over other than the fact that AMD stuck with their usual black PCB for the HD 7870.

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In terms of overall length, the 9 ¾” HD 7870 sits right between the HD 7950 and HD 7770 but will still fit into any ATX chassis without an issue. We’re sure to see custom versions at or soon after launch that either add to or reduce this size. Speaking of which….

At launch, don’t expect to see many reference versions on the market. As you can see above AMD’s board partners have decided to go with a wide variety of custom heatsinks, pre overclocked clock speeds and upgraded components for their HD 7870 product stacks. We should be reviewing many of these as official retail ability draws near.

 

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A Closer Look at the HD 7850 2GB

A Closer Look at the HD 7850 2GB

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Our HD 7850 2GB sample looked exactly like the HD 7870 with the only exception being the inclusion of a single 6-pin PCI-E connector. Otherwise, everything from the video outputs to the single Crossfire connector was identically. But not so fast….this is what the HD 7850 will actually look like in its “reference” guise:

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The HD 7850 will be built upon the same PCB we saw in the HD 7770 review and will use an identical heatsink setup with a centrally mounted 80mm fan pushing down onto a simple heatpipe cooler. Its length will be a compact 8 ¼” and the single power connector will be fed through the back area of the heatsink shroud.

Due to the condensed timeframe for launch, AMD seeded their media partners with a reference analog rather than the final design. Once the actual reference card becomes available, we’ll be sure to review it.

Much like the HD 7870, the HD 7850’s product stack will include very few top to bottom reference cards as board partners vie for market positioning. Most will come with custom heatsinks while a few will also include higher clock speeds and custom component layouts.

 

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Test System & Setup / Benchmark Sequences

Main Test System

Processor: Intel Core i7 920(ES) @ 4.0Ghz (Turbo Mode Enabled)
Memory: Corsair 3x2GB Dominator DDR3 1600Mhz
Motherboard: Gigabyte EX58-UD5
Cooling: CoolIT Boreas mTEC + Scythe Fan Controller
Disk Drive: Pioneer DVD Writer
Hard Drive: Western Digital Caviar Black 2TB
Power Supply: Corsair AX1200
Monitor: Samsung 305T
OS: Windows 7 Ultimate N x64 SP1


Acoustical Test System

Processor: Intel 2500K @ stock
Memory: G.Skill Ripjaws 8GB 1600MHz
Motherboard: Gigabyte EX58-UD5
Cooling: Thermalright TRUE Passive
SSD: Corsair Performance Pro 256GB
Power Supply: Seasonic X-Series Gold 800W


Drivers:
AMD Beta for HD 7800-series (8.932.2)
AMD 12.1 WHQL
NVIDIA 295.73 WHQL

Application Benchmark Information:
Note: In all instances, in-game sequences were used. The videos of the benchmark sequences have been uploaded below.


Battlefield 3

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Crysis 2

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Deus Ex Human Revolution

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Dirt 3

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Metro 2033

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Shogun 2: Total War

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Witcher 2 v2.0

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*Notes:

- All games tested have been patched to their latest version

- The OS has had all the latest hotfixes and updates installed

- All scores you see are the averages after 3 benchmark runs

All IQ settings were adjusted in-game and all GPU control panels were set to use application settings

 

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3DMark 11 (DX11)

3DMark 11 (DX11)

3DMark 11 is the latest in a long line of synthetic benchmarking programs from the Futuremark Corporation. This is their first foray into the DX11 rendering field and the result is a program that incorporates all of the latest techniques into a stunning display of imagery. Tessellation, depth of field, HDR, OpenCL physics and many others are on display here. In the benchmarks below we have included the results (at default settings) for both the Performance and Extreme presets.

Performance Preset

Extreme Preset

 

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Battlefield 3 (DX11)

Battlefield 3 (DX11)

For this benchmark, we used a sequence from the Rock and Hard Place mission. The results may seem lower than normal and this is due to the fact that after playing through the game multiple times, this one are was found to be the most demanding on the GPU. As with all of the tests, we try to find a worst case scenario in order to ensure a given card can properly play through the whole game instead of just a “typical” section.

1920 x 1200

2560 x 1600

 

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Crysis 2 (DX11)

Crysis 2 (DX11)

Crysis 2 with the DX11 and Texture Package installed not only looks great but it is a strain on any GPU. For this benchmark, we used a classic runthrough which includes far views, explosions, combat and close-in knifing; basically every hallmark of gameplay.

1920 x 1200

2560 x 1600